Struct bevy::ecs::prelude::Added

pub struct Added<T>(/* private fields */);
Expand description

A filter on a component that only retains results the first time after they have been added.

A common use for this filter is one-time initialization.

To retain all results without filtering but still check whether they were added after the system last ran, use Ref<T>.

Note that this includes changes that happened before the first time this Query was run.

§Deferred

Note, that entity modifications issued with Commands are visible only after deferred operations are applied, typically at the end of the schedule iteration.

§Time complexity

Added is not ArchetypeFilter, which practically means that if the query (with T component filter) matches a million entities, Added<T> filter will iterate over all of them even if none of them were just added.

For example, these two systems are roughly equivalent in terms of performance:


fn system1(q: Query<&MyComponent, Added<Transform>>) {
    for item in &q { /* component added */ }
}

fn system2(q: Query<(&MyComponent, Ref<Transform>)>) {
    for item in &q {
        if item.1.is_added() { /* component added */ }
    }
}

§Examples


fn print_add_name_component(query: Query<&Name, Added<Name>>) {
    for name in &query {
        println!("Named entity created: {:?}", name)
    }
}

Trait Implementations§

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impl<T> QueryFilter for Added<T>
where T: Component,

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const IS_ARCHETYPAL: bool = false

Returns true if (and only if) this Filter relies strictly on archetypes to limit which components are accessed by the Query. Read more
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unsafe fn filter_fetch( fetch: &mut <Added<T> as WorldQuery>::Fetch<'_>, entity: Entity, table_row: TableRow, ) -> bool

Returns true if the provided Entity and TableRow should be included in the query results. If false, the entity will be skipped. Read more
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impl<T> WorldQuery for Added<T>
where T: Component,

SAFETY: fetch accesses a single component in a readonly way. This is sound because update_component_access adds read access for that component and panics when appropriate. update_component_access adds a With filter for a component. This is sound because matches_component_set returns whether the set contains that component.

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type Item<'w> = bool

The item returned by this WorldQuery For QueryData this will be the item returned by the query. For QueryFilter this will be either (), or a bool indicating whether the entity should be included or a tuple of such things.
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type Fetch<'w> = AddedFetch<'w>

Per archetype/table state used by this WorldQuery to fetch Self::Item
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type State = ComponentId

State used to construct a Self::Fetch. This will be cached inside QueryState, so it is best to move as much data / computation here as possible to reduce the cost of constructing Self::Fetch.
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fn shrink<'wlong, 'wshort>( item: <Added<T> as WorldQuery>::Item<'wlong>, ) -> <Added<T> as WorldQuery>::Item<'wshort>
where 'wlong: 'wshort,

This function manually implements subtyping for the query items.
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unsafe fn init_fetch<'w>( world: UnsafeWorldCell<'w>, _: &ComponentId, last_run: Tick, this_run: Tick, ) -> <Added<T> as WorldQuery>::Fetch<'w>

Creates a new instance of this fetch. Read more
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const IS_DENSE: bool = _

Returns true if (and only if) every table of every archetype matched by this fetch contains all of the matched components. This is used to select a more efficient “table iterator” for “dense” queries. If this returns true, WorldQuery::set_table must be used before WorldQuery::fetch can be called for iterators. If this returns false, WorldQuery::set_archetype must be used before WorldQuery::fetch can be called for iterators.
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unsafe fn set_archetype<'w>( fetch: &mut <Added<T> as WorldQuery>::Fetch<'w>, component_id: &ComponentId, _archetype: &'w Archetype, table: &'w Table, )

Adjusts internal state to account for the next Archetype. This will always be called on archetypes that match this WorldQuery. Read more
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unsafe fn set_table<'w>( fetch: &mut <Added<T> as WorldQuery>::Fetch<'w>, _: &ComponentId, table: &'w Table, )

Adjusts internal state to account for the next Table. This will always be called on tables that match this WorldQuery. Read more
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unsafe fn fetch<'w>( fetch: &mut <Added<T> as WorldQuery>::Fetch<'w>, entity: Entity, table_row: TableRow, ) -> <Added<T> as WorldQuery>::Item<'w>

Fetch Self::Item for either the given entity in the current Table, or for the given entity in the current Archetype. This must always be called after WorldQuery::set_table with a table_row in the range of the current Table or after WorldQuery::set_archetype with a entity in the current archetype. Read more
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fn update_component_access( _: &ComponentId, access: &mut FilteredAccess<ComponentId>, )

Adds any component accesses used by this WorldQuery to access. Read more
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fn init_state(world: &mut World) -> ComponentId

Creates and initializes a State for this WorldQuery type.
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fn get_state(components: &Components) -> Option<ComponentId>

Attempts to initialize a State for this WorldQuery type using read-only access to Components.
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fn matches_component_set( _: &ComponentId, set_contains_id: &impl Fn(ComponentId) -> bool, ) -> bool

Returns true if this query matches a set of components. Otherwise, returns false. Read more
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fn set_access(_state: &mut Self::State, _access: &FilteredAccess<ComponentId>)

Sets available accesses for implementors with dynamic access such as FilteredEntityRef or FilteredEntityMut. Read more

Auto Trait Implementations§

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impl<T> Freeze for Added<T>

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impl<T> RefUnwindSafe for Added<T>
where T: RefUnwindSafe,

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impl<T> Send for Added<T>
where T: Send,

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impl<T> Sync for Added<T>
where T: Sync,

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impl<T> Unpin for Added<T>
where T: Unpin,

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impl<T> UnwindSafe for Added<T>
where T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T, U> AsBindGroupShaderType<U> for T
where U: ShaderType, &'a T: for<'a> Into<U>,

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fn as_bind_group_shader_type(&self, _images: &RenderAssets<GpuImage>) -> U

Return the T ShaderType for self. When used in AsBindGroup derives, it is safe to assume that all images in self exist.
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> Downcast<T> for T

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fn downcast(&self) -> &T

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impl<T> Downcast for T
where T: Any,

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fn into_any(self: Box<T>) -> Box<dyn Any>

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait.
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Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
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Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s.
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fn from_sample_(s: S) -> S

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Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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const ALIGN: usize = _

The alignment of pointer.
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type Init = T

The type for initializers.
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